This invention relates to a back-focus adjusting device for a video camera. In a conventional video camera which is provided with an interchangeable lens, when mounting the lens on a camera body, a distance between a lens mounting surface of a lens mount and an image pickup element built in a camera body needs to be set for a back-focus of the lens order to achieve a required resolution.
Namely, firstly, the image pickup element is fixed in the camera body, while the lens mount is assembled in the camera body in such manner as to be movable back and forth. Secondly, with the lens mounted on the lens mount, the lens mount is rotated to move back and forth along the optical axis. Thirdly, the lens mount is fixed with a set screw in such a position that a clear image of an object is formed on the image pickup element through the lens.
As mentioned above, according to the conventional video camera, the lens mount must be rotated with the lens mounted thereon to adjust the back focus of the lens. In particular, the lens which has a motor built therein to drive an iris diaphragm is heavy and bulky. Further, in such a lens a cord is pulled out from the motor. Thus, it is extremely troublesome to adjust a distance to which the lens mount moves by a minute rotation of lens.
Further, because video surveillance cameras are usually installed at corners of ceilings, or places which are difficult to operate the lens mounts, it is extremely difficult to adjust a back-focus of the lens by rotating the lens and the lens mounts, with the video surveillance camera installed at the corner of the ceiling or the like.